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Not Applicable
Spinal fusions are performed to treat degenerative diseases, deformities, and trauma. These problems generally cause or allow displacement or rotation of a vertebra relative to the adjacent vertebra. The objective of spinal implants is to facilitate realignment and/or fixation of spinal elements for fusion. In clinical studies it has been demonstrated that surgeries using spinal implants are more effective at providing structure and rigidity to the spine than surgeries in which implants are not used. Since their introduction as crude plates, rods, and wires, these devices have been developed into sophisticated appliances, which can be assembled and configured to rigidize spines of any size or condition. These devices provide a mechanical fixation for restraint of an implanted graft material. With this fixation, displacement of the disc graft material is significantly reduced. The majority of existing lumbar implants use round rods with pedicle screws threaded into the vertebra and clamped to the rod. Round rod assemblies use clamps or set screws to fix collars to the round rods. Round attachments tend to rotate around round rods and they depend on friction to resist torsion. These components are less rigid in torsion. Rectangular shaped devices better lend themselves to restrict rotational motion. The devices have been costly due to the complexity, which requires accurately machined components. Many of the existing devices require bone screw anti-rotational stops or locks to prevent the bone screw from unscrewing from the bone. Recent studies as well as time honored principles (Wolff""s Law), have shown that a device, that will allow the fusion joint to remain in compression, will tend to lessen distraction and reduce the fusion time. In the literature this motion is referred to as xe2x80x9cdynamizedxe2x80x9d motion. It is believed that compression will reduce the fusion time by reducing the stretching rupture and shear of the forming nutrient blood vessels.
Over time anterior or posterior spinal implants, which are stabilized with fixed rigid constructs have resulted in graft and implant failure and breakage. This is due to stress shielding of the healing bone by the rigid construct. Axial stress shielding results in failure of the bone to heal (failure of fusion), or development of a weak fusion unable to support the full physiologic forces. Semi rigid constructs have been developed to allow partial loading of the healing bone. These semi-rigid implants allow semi-rigidity in all 6 planes of motion thereby allowing harmful shear motion as well. Shear motions destroy the ingrowing nutrient vessels and can result in graft failure. Most semi rigid systems available are poor at allowing axial subsidence thereby poor at load sharing. To reduce the occurrence of axial stress shielding (thereby increasing load sharing by the graft), better implant devices are needed. These devices should collapse or freely move axially to allow normal linear subsidence of the vertebra and the graft, but still restrict motion in shear directions. These devices should allow the total load from the ligament tension and the weight above the graft to act upon the fusion interface resulting in a higher fusion rate and stronger fusion development. These devices are sometimes referred to as xe2x80x9cdynamicxe2x80x9d or xe2x80x9cdynamizedxe2x80x9d. The following patents are typical of other patents in this field:
Steffee (U.S. Pat. No. 4,719,905) describes an apparatus including a rod, clamps, and fastener assemblies for securing the rod to a spinal column.
Puno et al. (U.S. Pat. No. 4,805,602) utilizes an apparatus for the internal fixation of the spine. The apparatus includes two sets of implants each consisting of a rod and vertebral anchors.
Heinig et al. (U.S. Pat. No. 4,887,595) describes a plate and screw system for maintaining the relative position of the spinal bodies of a spinal column.
Sherman (U.S. Pat. No. 4,887,596) describes a pedicle screw for use in internal fixation of the spine.
Asher et al. (U.S. Pat. No. 5,084,049) describes a pair of corrective devices for securement to a spinal column. Each device includes a spine plate having a plurality of openings for receiving a fastener to connect the spine plate to a vertebra
Dubousset (U.S. Pat. No. 5,147,360) describes a device for correction of spinal curvature with anterior and posterior rods are fixed to the vertebral bodies to apply the necessary corrective forces to the spinal column.
Cotrel (U.S. Pat. No. 5,154,719) describes an implant for osteosynthesis, the implant being in the form of a screw having a rod-receiving head.
Mehdian (U.S. Pat. No. 5,217,497) describes an implant for fixing one segment of a spinal column to another segment, the implant in the form of a screw having a slotted head to which a support rod is anchored.
Ashman (U.S. Pat. No. 5,242,445) describes an eyebolt having two shell-like portions for engagement to a spinal rod.
Vignaud et al. (U.S. Pat. No. 5,261,907) describes an interconnecting device able to lock two spinal fasteners.
Wagner (U.S. Pat. No. 5,334,203) describes a construct using surgical rods and connectors. The connector includes a plate with a pair of double hook bolts to secure the plate to the surgical rods.
Engelhardt et al. (U.S. Pat. No. 5,613,967) describes an apparatus with a slotted plate with pedicle screws which are clamped together with an interference fit which will not allow free subsidence and stress shields all six motions.
Martin (U.S. Pat. No. 5,672,175 describes an implant places a constant force upon the vertebra to correct orthosis. This device does not give shear stress shielding required for fusion.
Many patents have been issued for spinal fixation devices, however none have the free 12 subsidence dynamized action feature. Most of these devices use a rod or a plate with pedicle screws threaded into the vertebra. They mainly differ in the mechanical means to attach the screws to the to the rods or plates. Many enable the surgeon to selectively adjust the alignment of the patient""s spine and then to secure that alignment with the spine fixation device. Further, due to the wide variation in spinal dimensions and availability of suitable attachment sites, most devices have limited application.
It would be a significant improvement to provide a spinal fixation apparatus and methods that would allow normal subsidence with the total force acting in axial compression on the graft, but would give stress shielding in the other five motions. It should allow the surgeon to select the vertebrae that require dymization and easily and quickly implement it. Such a novel spinal fixation apparatus and method is disclosed and claimed in this patent
This invention relates to an improved spinal stabilizing device, and a method of implanting it on the posterior, anterior, or lateral side of the lumbar spine. This device employs rectangular plate sections that allow axial subsiding motion without rotation and will allow continuous axial load sharing with the implant, without the need for accurately machined components. It is easily adapted and manipulated to fix the vertebrae or allow selected axial subsiding motion by the surgeon at the time of implantation. This device comprises a plate, bone screws, bone screw clamp portions, spacers, and rigidizing-stop locks. The bone screw clamp portions may be clamped firmly to the plate for a fully rigid system. Alternatively the screw clamp portions may be held apart, with clearance between them and the plate, by selectively installing clamp spacers. These spacers will allow for bone screw axial motion with respect to the plate, allowing for dynamized motion and load sharing. Compression clamping allows maintenance of compression. This allows only subsidence and prevents potentially damaging distraction of the graft vertebral interface. This contact interface is crucial to graft ingrowth of nutrient vessels. Described is a lumbar system connected by a pedicle screw construct. The pedicle screws and plates are not the focus of this patent and are considered as prior art.